1. Field of the Invention
The invention relates generally to wall structures having enhanced sound insulating or absorbing properties, and more particularly to acoustical doors having interior sound damping spaces or voids.
2. Reference to Prior Art
Acoustical wall structures such as doors, wall panels and the like are intended to minimize sound transmission therethrough to insulate a space from outside noise. Sound insulating wall structures can be constructed with considerable mass to reduce sound transmission. However, the use of heavy wall structures to achieve adequate sound insulating properties is often uneconomical or impractical. An example of a more economical lightweight acoustical door construction is illustrated in U.S. Pat. No. 4,998,598 issued Mar. 12, 1991. That acoustical door has multi-layered door panels each having an outer layer of plywood veneer, an inner layer of hardboard, and an intermediate layer of vinyl. The door panels are glued to a frame to enclose an air space that is completely filled with a fibrous sound absorbing material.
It is known to provide lightweight wall constructions with sound damping or absorbing interior air gaps or spaces to achieve sufficient sound insulating properties. Examples of such wall constructions are provided in U.S. Pat. No. 2,085,436 issued Jun. 29, 1937, U.S. Pat. No. 2,116,270 issued May 3, 1938, and U.S. Pat. No. 2,614,295 issued Oct. 21, 1952. In particular, U.S. Pat. No. 2,085,436 illustrates a soundproof wall or partition. The construction of the partition is somewhat complicated and includes opposite side panels separated by wooden posts to provide a sound absorbing dead air space in which an intermediate panel or core made of sound absorbing loose fibrous material is positioned. Each of the side panels has a multiple ply construction including an outer ply made of compressed wood fibers, an intermediate felt ply separated from the outer ply by an air space, and an inner ply of compressed wood fibers separated from the intermediate ply by another air space. The air spaces in the side panels are provided by individually attaching the plies to successively stepped portions of a panel framework. Thus, the plies are different sizes to fit within the windows formed by the corresponding stepped frame portions.